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Proceedings of the Nutrition Society
The Nutrition Society Summer Meeting 2015 held at University of Nottingham, Nottingham on 6–9 July 2015
Conference on ‘The future of animal products in the human diet: health and
environmental concerns’
Symposium 3: Alternatives to meat
Aquaculture: a rapidly growing and significant source of sustainable food?
Status, transitions and potential
D. C. Little
1
*, R. W. Newton
1
and M. C. M. Beveridge
1,2
1
Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, UK
2
Fisheries and Aquaculture Department, FAO, Via Delle Terme di Caracalla, 00153 Rome, Italy
The statusand potential of aquaculture is considered as part of a broader food landscape ofwild
aquatic and terrestrial food sources. Therationale andresource base required for thedevelopment
of aquaculture areconsidered in the context of broader societal development, cultural preferences
and human needs. Attention is drawn to the uneven development and current importance of
aquaculture globally as well as its considerable heterogeneity of form and function compared
with established terrestrial livestock production. The recent drivers of growth in demandand pro-
duction are examined and the persistent linkages between exploitation of wild stocks, full life cycle
culture and the various intermediate forms explored. An emergent trend for sourcing aquaculture
feeds from alternatives to marine ingredients is described and the implications for the sector with
rapidly growing feed needs discussed. The rise of non-conventional and innovative feed ingredi-
ents, often shared with terrestrial livestock, are considered, including aquaculture itself becoming
a major source of marine ingredients. The implications for the continued expected growth of
aquaculture are set in the context of sustainable intensification, with the challenges that conven-
tional intensification and emergent integration within, and between, value chains explored. The
review concludes with a consideration of the implications for dependent livelihoods and projec-
tions for various futures based on limited resources but growing demand.
Aquaculture: Fisheries: Nutritional significance: Resources: Societal impact
Aquaculture, the husbandry and farming of aquatic ani-
mals and plants, has expanded faster in recent decades
than any other livestock sector. It achieved a 7·5%annual
growth rate between 1990 and 2009, eclipsing the rapid
growth rates of the pig (<2·5 %) and poultry (<5 %) sec-
tors
(1)
. In comparison, the overexploitation of wild fishery
stocks has led to their contribution to world food stocks
flat-lining. Approximately 30 % are overfished, more than
60 % fully fished and <10 % have remaining capacity
(2)
.
In response to expanding demand from growing and better
off populations, the rise of aquaculture has beentimely but
its development has not been evenly distributed nor without
criticism, especially regarding environmental and social
impacts
(1,3,4)
. The characteristics of aquaculture, growing
rapidly from an artisanal and marginal activity, unknown
in most of the World, to a position where there are now
major complementarities and, potentially, resource alloca-
tion conflicts with terrestrial livestock and conventional
fisheries are reviewed in the present paper. Aquatic pro-
ducts, ‘fish’, often remain neglected in the current discourse
regarding food security
(5)
despite its importance in world
trade, human nutrition and support for livelihoods more
broadly. This theme is also explored in the paper.
Why farm? The continuance of wild fisheries in seafood
supplies
‘The motivations for people in traditional societies to
begin farming fish and shellfish are lost in time but an
*Corresponding author: D. C. Little, email dcl1@stir.ac.uk
Proceedings of the Nutrition Society (2016), 75, 274–286 doi:10.1017/S0029665116000665
© The Authors 2016
Proceedings of the Nutrition Society
assessment of terrestrial farming may offer some clues’.
The agricultural economist Ester Boserup
(6)
would answer
that farming began because ‘it was necessary’or as an-
other observer noted ‘People did not invent agriculture
and shout for joy. They drifted or were forced into it, pro-
testing all the way’
(7)
. It was also, likely, a gradual process.
Certainly, the transition from hunting to farming of terres-
trial food occurred over a longer time frame and geog-
raphy than that for aquatic products. A process of
proto-agriculture characterised by an opting in and out
of plant and animal cultivation depending on need, and
coaxing more food out of the environments depending
on need was part of a broader repertoire of responses to
times when demands for wild foods outstripped supplies.
Beveridge and Little
(8)
made a parallel case for the likeli-
hood of such proto-aquaculture occurring in the same
way it has for agriculture. It is clear that aquaculture
began independently and at various times in different
parts of the world and at several points along the aquatic
food supply line, between water and plate. The farming
of fish and shellfish is by definition an activity of settled so-
cieties, originating among both fishing and wetland farm-
ing cultures as well as at points of trade. It seems also to
have not been exclusively about food provision;
Beveridge and Little
(8)
found that historically in some con-
texts culture and religion were often powerful motivations
to invest in fish culture and the same has been demon-
strated in some contemporary experience
(9)
.
Since the end of World War II growth of global fish
(fish + shellfish) supplies have outstripped population
growth, effectively increasing annual per capita supplies
from 9·9 kg in the 1960s to 18·4 kg in 2009
(10)
. Growth
has been fuelled by rising demand for livestock and
fish, the result of increased economic access, changes in
trade policies and market liberalisation, urbanisation
and marketing
(11)
. During the first half of the post-war
period increases in fish supply came from capture
fisheries, thanks to massive private and public invest-
ments that resulted in a proliferation of larger, more ro-
bust and increasingly mechanised fishing craft and more
effective means of locating, catching and preserving fish
until landed
(12)
. By the late 1970s, however, the majority
of fish stocks was fully or overexploited
(13)
. Today, cap-
ture fisheries is dominated in production and employ-
ment terms by small-scale artisanal tropical fisheries.
While aquaculture accounted for only 3–6 % of global
fish supplies in the 1970s in the subsequent decades it
has consistently been among the fastest growing animal
source food sectors, to the extent that one fish in two
now consumed is farmed
(2,4)
. Any future expansion of
supplies must come from aquaculture.
Fisheries currently sustain the livelihoods of more than
40 million full-time and part-time fishers directly, an esti-
mated 90 % of whom are small-scale or artisanal and the
balance in industrial sector. Furthermore, an estimated
120 million are supported through fisheries-related activ-
ities, through employment in value chains etc. In contrast
more than one-third, or approximately 1 billion people,
are employed in agriculture globally. In poorer counties,
the proportion of employment is higher, reaching 60 % in
sub-Saharan Africa
(14)
.
The phrase ‘the livelihood of last resort’has been
coined for fisheries, and the concept of deteriorating
fisheries being a poverty trap is supported by recent stud-
ies. Cinner et al.
(15)
identified the poorest fishers as the
least likely to exit from a fishery in decline, although glo-
bally fishing is regarded as a traditional and noble occu-
pation that may be passed down through generations.
Amongst the rural poor, fishing activity may decline in
favour of alternative income generating activities but
not cease totally and fishers may be especially reluctant
to cease if they have significant investment in fishing ves-
sels and gear
(15)
. The availability of alternative livelihood
opportunities has been recognised as a key step and
aquaculture has been identified as a possible option.
However, this has given variable results, depending on
how lucrative the diversification strategies are in com-
parison with fishing. Seaweed farming in the
Philippines, for example, has produced mixed results
(16)
.
Fishing may be preferred because of its ability to provide
occasional very high returns in comparison with activities
such as seaweed farming that are unproven in terms of
providing long-term security. The viability of a small-
scale seaweed culture operation is governed by many of
the same challenges as other small-scale aquaculture
initiatives, including the availability of quality seed
(17)
and access to lucrative markets
(18)
. Seaweed farming
can be particularly labour intensive and there are still
significant technical hurdles for many species. Sheriff
et al.
(19)
found that the success of grouper and Asian
sea bass cage farming by fishers in southern Thailand
was dependent on a number of factors, including access
to credit and the substitution of financial for natural cap-
ital. The factors that have led to the persistence of
fisheries and varied development of aquaculture are
now considered.
Modern emergence of aquaculture: an uneven picture
Opportunity rather than necessity has arguably been the
major driver of modern aquaculture, which only has a
history of four to five decades with major increases in
the past two decades. Some key exceptions aside, the
rapid growth in aquaculture has been linked as much
to broader, the so-called ‘immanent’development, than
specific innovations
(20)
. Increased human population,
but more importantly increasing wealth and per capita
consumption of fish, especially in wealthier Western
countries, has driven incentives for aquaculture as an en-
terprise at a household and increasingly at the corporate
level. Urbanisation has made self-sourcing impractical
for most, fuelling the trade in fish as a commodity.
Historically fish culture has often been a peri-urban phe-
nomenon, driven by easy access to inputs and mar-
kets
(21)
. In contrast, rural populations in South and
Southeast Asia traditionally secured aquatic products
with little to no effort, as an output of wetland-based
agroecosystems
(22,23)
. Flooded rice-fields produce a
large variety and significant volumes of aquatic animals
as co-products and efforts to diversify away from rice
monoculture typically resulted in deeper pond areas
(24)
.
Aquaculture: a rapidly growing and significant source of sustainable food? 275
Proceedings of the Nutrition Society
Smallholder production in such systems
(23)
has
responded to increased demand and seasonal shortfalls,
often evolving into commercially orientated but still
largely household managed systems in Asia
(25)
. These in-
clude shrimp production that has grown strongly in the
past three decades since hatchery juveniles have become
available, in spite of disease-related setbacks. The sector,
dominated by two species, Litopenaeus vanammei and
Penaeus monodon, remains characterised by a large
range of production systems and culture intensities. In
contrast, the farming of Atlantic salmon (Salmo salar),
another global industry, is characterised by its highly
standardised cage-in-coastal water production system.
Growing at an average annual rate of 16 % since 1985,
Norweigan interests dominate globally, producing more
than 50 % of the total harvest in-country
(26)
and with
significant interests elsewhere (Canada, Chile,
Scotland). Developing international trade for such spe-
cies has driven transformation further and in the case
of salmon led to consolidation of production among
fewer larger enterprises
(26,27)
. Improved productivity of
larger farms, increasing levels of specialisation of produc-
tion and refined regulation have all contributed to con-
solidation, for which there is a general emergent trend
across the seafood sector. Österblom et al.
(28)
identified
thirteen lead firms in the sector, more than half of
which were located in the Asia Pacific region, badging
them as keystone actors because of their analogy to the
disproportionate impact that keystone species in ecosys-
tems exert on ‘ecosystems’. These keystone actors cur-
rently control 11–16 % of the global marine catch and
19–40 % of the most important stocks, including
Alaskan pollock (Gadus chalcogrammus) and various
tunas. The thirteen firms include the top two fishmeal
and fish oil producers, 68 % of salmon and 35 % of
shrimp feed producers, as two of the most reliant sectors
on fishmeal and fish oil, and therefore exert an influence
at both ends of the food chain.
Ensuring aquaculture is sustainable or at least respon-
sible has become a key driver for OECD (Organisation
for economic co-operation and development) economies,
particularly in North America and Europe, and private
sector governance where certification, offered by a
range of organisations, has emerged as a major force.
This contrasts with the major centre of production and
consumption, the Asia Pacific region, for which national
and intraregional trade remains largely outside such stan-
dards
(29)
. Production in farmed carps, catfish and tilapias
has grown strongly in this region and probably constitu-
tes more than 80 % of global fin-fish aquaculture (Fig. 1).
Growth of major carps and tilapias is especially strong
and is likely to dominate growth into the near future
(Fig. 2). The sustainable intensification of such lower
trophic species, especially in terms of the feed ingredients
used in their diets, warrants at least as much attention as
the critical focus on salmonids and shrimp to date and
this is considered in a later section.
The rapid growth in aquaculture in some parts of the
world suggests that technical barriers can be overcome
given the right context for development and is often
achieved largely by commercial actors. However, recent
history suggests that a pioneer development phase can
occur without significant levels of conventional research,
as demonstrated by the rapid growth of the striped
catfish (Pangasianodon hypophthalmus) sector in Vietnam
between 2000 and 2008 that outpaced Norwegian salmon
production, with only a fraction of the research and devel-
opment investment (Fig. 3). The recent decline in striped
catfish outputs reflects market constraints rather than sign-
ificant technical challenges and the fish remains highly
competitive in global white fish markets; investment in re-
search at this point is likely to have impressive returns in
terms of profitability. These examples, however, contrast
with those where aquaculture, as either a subsistence or
commercially orientated activity, has developed far more
slowly or indeed has never become established, even
when supported by targeted assistance. A long and disap-
pointing history of promoting subsistence-orientated aqua-
culture in sub-Saharan Africa has been the subject of some
analysis
(30,31)
but aquaculture has generally failed to be
sustained, even where fish has dietary importance, in con-
texts as varied as Sri Lanka to Caribbean and Pacific
Islands
(32,33)
. Failure has been linked to a misunderstand-
ing of demand and, often, a lack of any competitive advan-
tage of start-up aquaculture enterprises with established
fisheries. The global aggregate decline in importance of
fisheries obscures important local differences. The
European Union continues to rely massively on wild
catches, of which a substantive proportion is imported
(60 % of the overall seafood supply)
(34)
. because of substi-
tution of cheaper products from local fisheries and
imported wild and cultured products.
Generalised aquaculture statistics also lead to the
wrong conclusions and disguise its real status. Just as
the aquaculture sector in Europe, with some exceptions,
has failed to grow, double digit growth characterises ex-
pansion in Asia. Drilling further down into the data,
however, shows that Atlantic salmon production is now
more important than beef in Scotland, at least as far as
total farm revenues are concerned
(35)
. Mediterranean sea
bass and bream production has hugely increased in
Turkey, whilst a boom in aquaculture has failed to materi-
alise in some countries in Asia, such as Malaysia, despite
Government support and rapid expansion in neighbouring
countries. More than 65 % of Indonesia’s massive output
are marine seaweeds, mainly supplying markets for hydro-
colloids (caregeenan) widely used in food processing, al-
though there has also been rapid growth of shrimp,
milkfish, tilapia and various catfish (Fig. 4).
Fig. 1. Global aquaculture production by volume in 2014
(42)
.
D. C. Little et al.276
Proceedings of the Nutrition Society
Furthermore, modern aquaculture development can
be characterised as another green rather than a blue revo-
lution, as most fish production occurs inland in fresh-
waters rather than the sea
(36)
. The reality thus
inevitably mutes the expectations of mariculture being
a panacea for food security since a reliance on terrestrial-
ly derived feed ingredients remains, which are heavily
constrained by land and fresh water availability
(37)
. The
exceptions to this ‘norm’are filter-feeding bivalves and
seaweeds, for which expanded production is not linked
to such constraints but which are still subject to market
and site availability factors.
Thus, the trends in seafood production are more com-
plex than often presented, as are the challenges to aqua-
culture becoming a major source of food and nutrition
where it is most required. An examination of the geog-
raphy of nutritional reliance on seafood can inform our
understanding of its spatial development, to which we
now turn.
The nutritional imperative
Seafood constitutes nearly 16 % of all global animal pro-
tein, more than 5 % of all protein and an estimated 4·5
billion people rely on seafood for 15 % or more of their
animal protein
(5)
. A conventional focus on protein in
diets has undervalued the key importance of fats, espe-
cially the highly unsaturated fatty acids, and micronutri-
ents of which seafood are concentrated sources
(38)
. The
dynamic trade in seafood has raised the issue of emerging
global inequity in terms of continued affordable and
available seafood given current trends
(4)
. The significant
diversity in current consumption of seafood (as a % of
animal protein) and spatial importance of aquaculture
as characterised by production intensity or contribution
to the economy suggests some important mismatches.
Although high production in South and Southeast Asia
corresponds with this being an area of high consumption,
the swathe of high consumption across west and central
Fig. 2. Growth of major aquaculture fin-fish species until 2014 and extrapolated
projections to 2030 (dotted line), millions of tonnes
(42)
.
Fig. 3. Norwegian salmon and Vietnamese catfish production, 2000–2014 along with
cumulative numbers of peer reviewed articles for each to 2016
(42)
.
Aquaculture: a rapidly growing and significant source of sustainable food? 277
Proceedings of the Nutrition Society
Africa is yet to be supported by high levels of indigenous
aquaculture, despite high growth since 2000
(2,4,39)
. Wild
stocks, mainly imported cheap marine pelagic species
and local freshwater fisheries, currently support most
consumption needs, but intensive aquaculture has now
become established in several areas of West Africa
(40,41)
and imports of farmed fish from China have also
accelerated
(42)
.
In terms of importance to overall economies, aquacul-
ture generally remains <2 % of gross domestic product,
with the exceptions of Bangladesh and Vietnam where,
relative to the economy as a whole, it is highly developed
and important (Fig. 5). The origins of aquaculture in
Asia have been linked to the importance of
aquatic-relative to terrestrial-derived food in densely
settled floodplains and estuarine deltas. Original sites of
aquaculture that have been sustained to the modern era
include the heavily populated river deltas of Southern
China and coastal ponds of Java
(8)
. In contrast popula-
tion densities have increased relatively recently in the
Mekong Delta
(43)
and Bangladesh
(44)
.
The consumption of aquatic v. terrestrial livestock pro-
ducts is a good indicator of their comparative dietary im-
portance and a rapid assessment of the number of food
vendors can be indicative, such as that conducted in
Kolkata (Fig. 6). Expenditure on fresh and preserved
fish exceeded that of all terrestrial meat combined in
one recent study in rural Cambodia
(46)
. In comparison
with terrestrial livestock products, and particularly for
poor consumers, processed forms of aquatic food are
often nutritionally critical. Their importance to food se-
curity through their roles in smoothing seasonality of
food supply and public health are often overlooked, or
perceived as public health risks because of their associ-
ation with parasites and/or adulterants of various
types
(47,48)
. Understanding how farmed and wild fish
fulfil different roles in the diet remains poor; typically,
even in areas where fish culture is well established, farm-
ers and non-producers continue to source and consume
both
(49,50)
. This has implications for livelihoods both
local to, and at distance from, production, and value
chain analysis is increasingly used as the lens to assess
Fig. 4. Aquaculture production in selected Southeast Asian countries in 2004 and 2014
(42)
.
Fig. 5. Global contribution of aquaculture to gross domestic product (GDP) by country
(107)
.
Fig. 6. Proportion of different food stuffs sold at market stalls in
Kolkata, India
(45)
.
D. C. Little et al.278
Proceedings of the Nutrition Society
such impacts
(51)
. It also prompts the issue of differentiat-
ing wild and farmed products, which is considered in the
following section.
Wild and farmed: the linkages
The relationship between wild stocks and farmed aquatic
animals remains closely intertwined. Most products end
up side by side on menus or on seafood displays, some-
times poorly identified or even the subject of fraudulent
claims
(52)
. Some farmed products depend on stocking
juveniles harvested from the wild or at least produced
from breeding animals removed from wild habitats.
Increasingly, farmers have moved towards closed cycle
production, whereby captive bred breeding animals pro-
duce juveniles under controlled conditions and are in-
creasingly the subject of selection, or other hatchery
techniques, to improve their performance. An important
proportion of the global harvest is produced from
so-called enhanced fisheries, where natural yields are
increased by stocking hatchery-produced juveniles and
the imposition of management rules
(53)
.
Both fattening of wild juveniles and enhanced fisheries
fall between closed cycle aquaculture and exploitation of
wild stocks but tend to target different consumers and
face different challenges.
Some of the world’s most expensive seafood is based
on harvest of wild juveniles before being farmed to a
finished product. Technical control of the whole breeding
cycle for the bluefin tuna (Thunnus oreintalis) and
European eel (Anguilla anguilla), despite significant pro-
gress, have yet to reach commercially viable levels
(54,55)
.
The harvest of juvenile European eels attracts significant
criticism and, as an endangered species, their harvest has
been made illegal in the European Union. In contrast,
some types of such capture-based aquaculture are widely
perceived as being low impact and sustainable, such as
the collection of spat for on growing of bivalves such
as the blue mussel (Mytilus edulis). In contrast the stock-
ing of hatchery produced juveniles in freshwater
impoundments, rivers and coastal waters, also known
as culture-based fisheries, has stabilised or improved ac-
cess to aquatic food for food insecure inland communi-
ties. Marine ranching has had a more mixed impact,
although forming the basis of major processing and ex-
port industries in the West Coast North America and
(canned Pacific salmon).
In contemporary debate, polarised positions are fre-
quently taken whereby aquaculture is framed as sustainable
and in ascent and fisheries unsustainable and in decline but
entrenched positions ensure that these are frequently chal-
lenged and that inverse positions are advanced
(3,56–60)
.
The sustainable status of aquaculture has often fo-
cused on a narrow Western view of aquaculture based
on mariculture of carnivorous species. Many farmed, es-
pecially the juvenile stages of carnivorous fish, species re-
main dependent on wild fish stocks processed as marine
ingredients (fishmeal and fish oil) for feed. As sustainable
catches of the small pelagic species that underpin the
major share of the global resource base have been
reached, marine ingredients represent a declining compo-
nent of most farmed fish diets as feed formulators seek to
substitute them with cheaper plant ingredients and im-
prove the functionality of the replacement products.
The arrival of lower trophic farmed species, which are
generally less dependent on marine ingredients, such as
striped catfish and tilapias, into the international seafood
trade in the last 10–15 years has also realigned the fish
in-fish out
(61)
relationship with steep declines in the levels
of marine ingredients commonly used in most aquacul-
ture diets
(61)
. The large differences in dietary dependence
are mostly related to interspecific differences in natural
feeding habit. Fishmeal consumption of farmed
Atlantic salmon still exceeds that of the omnivorous
striped catfish in Vietnam by more than a factor of
five
(62)
but inclusion levels are dropping quickly for
much of the industry. Innovation towards low and
non-fishmeal diets is dynamic, e.g. the recent announce-
ment for a commercial salmon fishmeal-free diet.
Innovation of this type is not uniform throughout the
sector, however. From a general but highly influential
critique of the use of marine ingredients in aquaculture
focusing on salmon and shrimp
(63)
, more recent and
specific analyses have turned to Asia and especially
China
(64)
. Such studies acknowledge progress and oppor-
tunities as well as threats associated with the rapid
growth and changing status of aquaculture.
The nature of the marine ingredients industry has
evolved in parallel with the fisheries and aquaculture in-
dustries. All three sectors have had to find efficiency sav-
ings through better utilisation of waste and other
resources, so that now an estimated 35 % of all marine
ingredients are sourced from fisheries and aquaculture
by-products that were previously treated as waste
(Marine Ingredients Organisation (IFFO)/University of
Stirling, unpublished results). The role of aquaculture it-
self becoming a major source of marine ingredients and
strategies to enhance their value is considered later.
Delinking aquaculture feeds from marine ecosystems
A decline in reliance on marine ingredients in feed, large-
ly because of their high unit costs, has been a major dri-
ver to change in the aquaculture sector. The increasing
influence of eco-standards on international trade is also
driving reductions in their use, although sustainability
concerns for terrestrial feed ingredients have attracted
less attention
(65)
. A major challenge is maintaining the
nutritional quality for human consumption of fish in
which vegetables, mainly n-6 oils, have substituted for
marine lipids, mainly n-3 oils
(66)
. A recent consumption
study
(67)
, however, demonstrated that even fish-fed diets
relatively low in fish oil (‘eco-diets’) nonetheless deliver
high nutritional outcomes. Longer term, the use of high
EPA-transgenic Camelina sativa oil may prove a viable
alternative to maintain availability of this vital ingredi-
ent
(68)
, provided it gains acceptance by regulators, retai-
lers and consumers. The search for alternative feed
ingredients continues (see e.g. https://www.foodsofnor-
way.net)
(69)
as for livestock in general, together with
Aquaculture: a rapidly growing and significant source of sustainable food? 279
Proceedings of the Nutrition Society
improved processing of ingredients and prophylactic
health strategies through use of pro and pre-biotics.
Novel ingredients such as insects show promise, although
this has yet to be demonstrated on a commercial scale
(70)
or gain regulatory approval in key markets. Potentially,
their role in adding value to wastes through production
of a quality feed ingredient can be achieved with minimal
competition for resources. Similarly, the use of waste or
low-value feedstocks for microbial and fungal protein
has resulted in mature technologies and products, some
of which already have full regulatory approval for use
in livestock feeds
(71)
or are already in the marketplace
supporting the move of shrimps away from reliance on
marine ingredients
(72)
. The higher relative interest in
these products by the aquatic rather than the terrestrial
sector reflects the former’s continued dependence on
high trophic species for marine ingredients. High trophic
aquatic animals have a comparatively high demand for
protein and also face a continuing challenge to inclusion
of high levels of dietary soya. The costs of alternatives
and the risks associated with investment at the necessary
scale are the key constraints to the use of these types of
ingredient
(71)
. Critiques of aquaculture frequently label
it as a high-impact food sector but farmed seafood typic-
ally shares supply chains for feed ingredients with terres-
trial livestock and actually consumes little more than 4 %
of the total used
(1)
. Life cycle assessments underline the
importance of feed to the overall environmental impacts,
including freshwater, land and greenhouse gas emissions
for all livestock, fed-aquaculture included
(37,73–77)
to an
extent that in many cases food conversion ratios may
be used as crude indicators of environmental impact.
Innovation to reduce impacts of feeds mostly occurs up-
stream at the levels of ingredient sourcing, production
and processing, but we now turn to environmental inter-
actions in and around the farm.
Environmental challenges at farm and landscape
Expectations that aquaculture would be a novel source of
highly nutritious food, thus relieving pressures on scant
terrestrial resources, have proved to be less revolutionary
than hoped. Like all human activities, aquaculture takes
resources which, using inputs of energy, capital and la-
bour, it transforms into products valued and traded by
society. Impacts may be split into those occurring direct-
ly at the farm and indirect impacts occurring throughout
the value chain, both up and downstream of production.
Aquaculture needs space on land or in coastal waters,
lakes or reservoirs in which to develop production sys-
tems. Water is needed both for physical support of
farmed aquatic animals and to supply oxygen and dis-
perse and assimilate wastes. Seed (spores, spat, post-
larvae, fry or fingerlings) is required to stock the systems,
and fertilisers and feeds must often be used to increase
production. Energy may be required to pump water
and aerate ponds, to import seed and feed onto the
farm and to process and transport produce to markets.
Wastes, uneaten food, faeces and metabolic wastes and
chemicals (including medicines), as well as escaped
organisms (including farm animals and pathogens), are
inevitably released, treated or untreated, into the envir-
onment. Farms, through their physical presence alone,
may also have an effect on ecosystem services and
biodiversity
(66)
.
Water use
The direct and indirect use of water, in contrast to terres-
trial livestock, does not always imply consumption.
Advocates of marine agronomy (marineagronomy.org)
point to the independence of salt tolerant plants from
limited freshwater supplies and the same is true for
filter feeding animals. However, fed fin-fish and crusta-
ceans both have varying dependencies on freshwater,
whether grown either in the marine or freshwater envir-
onment related firstly to feed provision and secondly to
environmental services. The water required for the envir-
onmental services; oxygen, support and dispersal of
wastes, remains mostly in the biosphere and may then be-
come unusable for other purposes such as for drinking
but may also be enhanced as a source of nutrition for
integrated agriculture or unaffected for use in indus-
try
(1,66,78)
. How usable it is may depend on the intensity
of aquaculture and the level of subsequent dilution.
Assuming that little water used for environmental ser-
vices is actually consumed
(66)
, it is usually far exceeded
by the amount required for provision of feed
(1,37)
.
Therefore, feed used to edible yield ratio is the key to
overall livestock production ratio and unfed systems,
such as marine molluscs, have a massive advantage
over all fed livestock in terms of freshwater and land
use. However, filter feeders can accumulate toxins from
their surrounding environment and under such condi-
tions require large amounts of energy to clean them
using pure water in depuration processes. In contrast
cage-farmed fish, such as Atlantic salmon, which still
have fishmeal and fish oil in their diets do not have
such post-harvest energy demands and have high edible
yield to harvested yield ratios. Shellfish also require
large quantities of energy on site for general maintenance
compared with fin-fish
(79)
. Large greenhouse gas emis-
sions related to energy could be mitigated by encour-
aging producers (e.g. reduced costs; tax breaks) to use
cleaner energy, such as from wind and solar technologies.
Intensification of aquaculture
The environmental impacts of aquaculture are largely
determined by species, system, production methods (i.e.
whether extensive, semi‐intensive or intensive), location
and quality of management. Biodiversity is closely asso-
ciated with the provision of ecosystem services
(39)
. More
product for less environmental impact, while retaining or
improving the high dietary value of farmed seafood and
ensuring high welfare outcomes for both the animals pro-
duced the people involve, are critical components of sus-
tainable intensification
(80,81)
. The environmental
imperative for aquaculture, whereby auto-pollution can
D. C. Little et al.280
Proceedings of the Nutrition Society
undermine productivity at the individual enterprise and
broader, zonal and even global levels of production,
has been a major incentive to rapid change in the sector.
Managing aquatic stocks within the carrying capacity of
the culture environment, well known to terrestrial pastor-
alists, has a particular significance for a fish farmer need-
ing to maintain both levels of nutrition and water quality
because of the acute impacts of any deterioration in the
latter on the survival and growth of the stock
(80)
.
Access to plentiful water at low-cost and good system de-
sign that allows for removal of solid wastes are critical,
but improvements in feeds and feed delivery that reduce
waste have also been transformative
(78)
. This includes
better nutritional formulation, pellet integrity and feed
systems, all of which have reduced waste and improved
feed efficiencies. Simple changes to earthen pond design
have increased productivity by a factor of three in
China, for example
(82)
. Poor solids removal has been a
common cause of failure in highly capitalised intensive
recirculation systems and a major focus for research
(83)
.
Generally, energy efficiency increases with intensifica-
tion, but access to consistent and affordable power for
aeration or pumping remains a key limitation to cost ef-
fective intensification in many contexts. Tropical coun-
tries may have advantages in their potential for using
solar power in transformations away from fossil-fuel-
based energy. Low- and medium-income countries have
often been less equipped to adapt to volatility in the fossil-
fuel sector
(84)
but there are implications for reliance on
various green energy supplies, including costs and reliabil-
ity. Overall, there are trade-offs between various impacts,
both environmental and social, and recently there have
been efforts to examine these interactions through a
‘nexus’approach that connects seemingly disparate objec-
tives with food security being the link between them
(85)
.
Aquaculture may compete with or complement agricul-
ture for nutrients, water land and energy. This is often related
to the nature of the aquaculture, particularly if it is integrated
within local food systems or develops as a specialised and
stand-alone activity. Detrimental effects may occur through
intensification of livestock and crop production that can pro-
duce environmental impacts on aquaculture and vice versa.
For example the use of agrochemicals in and around fish
farms or within rice–fish systems can have negative impacts
on survival and productivity of both farmed and wild
aquatic animals in receiving waters
(86)
.Management
approaches can be used to mitigate worst impacts and mod-
els of chemical behaviour can guide better practice
(87)
.
Intensive aquaculture, especially if occurring in geographic-
al clusters, can impact on surrounding water quality to the
detriment of both the aquaculture enterprise itself and
other water users
(88)
. Apart from poorer water quality
and its impact on performance, over development can
lead to rapid spread of disease and economic loss
(88)
.
Integrated approaches
A parallel trend to intensification of farmed seafood pro-
duction is integration occurring at different points in the
value chain.
Traditional forms of aquaculture typically developed
under conditions of nutrient scarcity and were often close-
ly integrated with other human activities through neces-
sity
(89)
. A general trend to intensification has rendered
many low-input traditional systems obsolete
(36)
,although
they are being used as templates for reducing the environ-
mental impacts of intensive aquaculture where surplus
nutrients (as wastes and by-products) can be recycled
through associated food production. This is equivalent
to the concept of ‘ecological leftovers’advanced by
Garnett
(90)
as a potential lens for increased sustainability
of livestock production. Central to integrated aquatic pro-
duction is the concept of farming filter feeding (non-fed or
extractive) species alongside fed species, and in some cases
aquatic plants that can take advantage of dissolved nutri-
ents that result from such high-input systems. Typically
the different components are quite separate enterprises,
the sharing of space and nutrients occurring on an infor-
mal or opportunistic basis. Commercial systems exist in
both freshwater and marine contexts, particularly where
they have co-evolved. Such systems are widespread in
coastal China. In recent years the concept, termed
Integrated multitrophic aquaculture
(91–93)
has become
the focus of research interest, particularly to mitigate the
environmental impacts of intensive salmonid cage culture.
Challenges remain to ensure the individual components
are economically viable especially within the very different
business enterprise and regulatory contexts of Europe and
North America.
Research into integrated mariculture, targeting the re-
tention and reuse of nutrients, is faced with the challenge
of dealing with saline effluents. Inland aquaculture is
more likely to be integrated with other forms of human
activity, however, either formally or informally.
Scarcity is ensuring that freshwater reuse is becoming in-
creasingly multipurpose, by default. Thus, cages in com-
mon property water bodies enrich water with nutrients
subsequently used for agriculture, and on-farm ponds
act as reservoirs to irrigate subsistence or cash food
crops nearby
(66)
. The practice of livestock waste disposal
in ponds is still common in many parts of the tropics,
even where high-quality fish feeds are available, as it
can reduce costs compared with complete feed-based
production and reduce risks associated with livestock
production. Risks to human health and potentially,
greater greenhouse gas emissions
(94)
, of waste-based
aquaculture need to be considered but both can be dra-
matically reduced through good design. Although use
of formulated diets to intensify production is a clear
trend, retention and in some cases reintroduction of poly-
cultures to produce a range of species in the same pond is
widespread
(95)
. Much of this tendency is related to redu-
cing risks and accessing local markets, although such
practices may also improve water quality and, subse-
quently, productivity gains for the system as a whole.
Whilst returns for the primary species remain critical,
the impacts on local food security of secondary species
harvested from such systems have often been ignored.
Intensification and integration are far from being mu-
tually exclusive. Although farm intensification has often
rendered the ability to horizontally integrate systems
Aquaculture: a rapidly growing and significant source of sustainable food? 281
Proceedings of the Nutrition Society
more difficult, it has opened opportunities through verti-
cal integration which were not common or efficient in
more traditional systems. The selling of by-products
from fish and shrimp processing is a prime example,
where previously volumes were too low, or products
undervalued, to make this viable, it is now common in
the salmon, tilapia, striped catfish and shrimp industries.
Nevertheless, in contrast to terrestrial livestock, seafood
processing is often linked to export markets, especially
in Asia. The industry for processing seafood by-products
thus still remains underdeveloped compared with its ter-
restrial counterparts.
By-product utilisation
Ultimately, the proportion of the animal that can be uti-
lised as food or indirectly in subsequent value chains is
critical to the overall profitability and environmental im-
pact. Markets are well established for all parts of terres-
trial animals, including for example leather, gelatin and
other food additives but less so for aquatic where much
of the by-product may be wasted or poorly utilised.
Where terrestrial animals are most frequently sold as
various portions or cuts, aquatic food may still often be
found sold live or with minimal processing.
Aquaculture itself, particularly through reuse of
by-products of processing, is becoming a major source of
fishmeal and oil. The trend is being encouraged by moves
to process fish close to source and making cost effective col-
lection and processing of a wide variety of by-products vi-
able. Hence, for striped catfish in Vietnam, stomachs and
belly flaps are used as direct human food locally. New mar-
kets for higher value products, such as collagen and gelatine
extracted from skin before frames and other remains are
processed into lower grade fishmeal used for pigs and
other fish production, are emerging
(96)
. Higher value protein
concentrates produced from processing wastes of salmon
and other high-value fish species are being developed for
disease-susceptible juvenile production in both aquaculture
and terrestrial livestock. Functional properties are being in-
creasingly claimed and demonstrated for such products in
both human and animal nutrition
(97–100)
.Intheshrimpin-
dustry, chitin from shell by-product is being directed to
manufacture various grades of chitosan that have wide
ranges of applications from waste water treatment to bio-
medical uses. The speed of change in adding value to farmed
seafood is remarkable and signifies the sector maturing and
becoming more competitive with other animal products.
Aquaculture and changing impacts on livelihoods
The motivation for developing any aquaculture enter-
prise is increasingly driven by commercial objectives.
Low input–low output, subsistence orientated aquacul-
ture remains common in some parts of the world, espe-
cially where fish is everyday food, such as in much of
Asia. Households still dependent on agriculture for
much of their income typically use their aquatic resources
as a ‘bank’strategically
(101)
; while selling or gifting some
of their crop they will also continue buying in fish from
the market and/or exploiting wild stocks. These
approaches can offer reasonable income and security at
a lower risk compared with high investments required
for intensification. Opportunities to supply lucrative mar-
kets, however, tends to encourage intensification and at-
tract entrepreneurs to the sector
(25)
, supported by the
development of a range of upstream and downstream ser-
vices. Growth in export-led markets from low- and
medium-income countries-based production, initially
for shrimp and more latterly for white fish species (tilapia
and striped catfish), has often transformed geographical
areas where it is concentrated. Clusters of production
and processing have become relatively prosperous, gener-
ally related to growth in employment opportunities in the
value chain as a whole. Such dynamism can also stimu-
late competition and quality improvement and the rise
of larger-scale commercial aquaculture. Smallholders
may, however, still persist in such contexts, for example
shrimp culture in Thailand, in parallel with company
and corporate development. Private sector standard de-
velopment with its inherent need for traceability is likely
to become a major factor in ensuring access to OECD
markets, although penetration to other markets has
scarcely begun
(29)
. Marginalisation of smaller-scale pro-
ducers and their exclusion from the more lucrative
value chains, such as has occurred in other sectors, is
considered a real threat. Collective action, assisted by dif-
ferent domestic and international organisations, includ-
ing the certifiers themselves, offers some hope that
smallholder producers can be retained in such global
value chains, although the speed of consolidation has
been rapid in some sectors. The striped catfish sector in
the Mekong Delta, Vietnam was transformed in less
than a decade from a smallholder system dependent on
local inputs (wild seed, human and pig manure, together
with home-made feeds) supporting local demand, to a glo-
bal producer of white fish, highly dependent on imported
feed ingredients. In general, research suggests that employ-
ment generated by commercially orientated, family farms
is likely to generate the greatest overall opportunities for
rural communities to escape poverty
(25)
. The trend to-
wards the global seafood trade, both wild capture and
aquaculture, being controlled by large integrated corpor-
ate entities is therefore an issue. The resilience of the family
farm, its decline much lamented but still dominant in over-
all food production
(102)
, suggests that the mosaic of con-
temporary aquaculture systems found throughout both
the richer and poorer world will persist.
Conclusions
The expected growth in both human population and per
capita consumption of farmed seafood, is linked to both
the decline in availability of wild stocks and growth in
urban-driven purchasing power. These drivers necessitate
an increase in both the scale and productivity of aquacul-
ture. Already characterised by a huge diversity of farmed
species, consolidation around fewer, genetically
improved strains and species with greater scientific
D. C. Little et al.282
Proceedings of the Nutrition Society
investment is likely in the decades ahead. Life cycle
assessments indicate even current stocks and systems
are comparable with, or better than most terrestrial live-
stock in terms of greenhouse gas, fresh water, land use
and other impacts
(37,77)
. This suggests the untapped po-
tential of aquatic animals has only just begun to be rea-
lised. The first steps, with selective breeding of farmed
Atlantic salmon, shrimp and tilapias, are well underway
and demonstrating potential, as is consideration of the
benefits of the basic efficiencies of farming coldblooded
animals. A review of change in basic feeding efficiencies
of the key aquaculture species (Table 1) in the past few
years suggests the rapid improvements made, on the
basis of feed, breed and management. This could be
expected to follow similar lines to broiler chicken devel-
opment
(103)
. A key question is where are these major
efficiencies most likely to be realised in a constantly mov-
ing food production landscape and the degree to which
the three major pillars of sustainability evolve and impact
on one another?
Current trajectories suggest that international trade in
farmed seafood will remain a key characteristic of the
sector given the advantages that tropical countries have
in terms of species and environments and the trend to-
wards consumption of processed, value-added products
worldwide. Well designed and managed ponds, where en-
vironmental impacts are minimised, have a large com-
petitive edge over more intensive technological
solutions such as tank-based recirculation systems that
have been developed for higher value species in OECD
countries. However, the species–farm environment inter-
action is also dependent on consumers’likely choices
going forward and different visions of food futures
(90)
.
The role of technological innovation in meeting the chal-
lenges facing the sustainable intensification of aquacul-
ture have been considered earlier, conventionally
categorised within the fields of ‘feeds, genes and disease’
but increasingly advances are being made at their inter-
face and in the context of limitations imposed by the
water–nutrient–energy nexus
(104)
.
Financial Support
David Little was supported by the Nutrition Society to
present an oral version of this paper at their Summer
Meeting 2015 at the University of Nottingham. Much
of the article derives from outcomes of the Sustaining
Ethical Aquaculture Trade project (no. 222889)
co-founded by the European Commission within
the Seventh Framework467 Programme—Sustainable
Development Global Change and Ecosystem for which
consortium members are acknowledged for their partici-
pation. The paper also serves as a contribution to the
FAO Committee on Fisheries Sub-Committee on
Aquaculture, which is working to determine the contri-
bution of aquaculture to food security and nutrition.
Conflicts of Interest
None.
Authorship
The concept and major contribution to this article was
prepared by D. L. Contributions to environment sections
and figures were prepared by R. N., while major contri-
butions to development sections were prepared by M. B.
All authors had oversight of the final document regard-
ing key messages and conclusions.
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